There was an interesting article yesterday in USA today about a study that used scans to reveal what was actually occurring in the brain undergoing a hypnotic suggestion of paralysis.
You can read the article here: http://www.usatoday.com/tech/science/2009-06-24-paralyzed-hypnosis_N.htm
Basically, as was commonly theorized, it was shown to be different from someone just imagining that their hand was frozen. Part of the brain thought to be responsible for mapping one’s own body is getting involved in the process. The motor cortex prepared to move the subject’s hand as it normally would, but the precuneus gets involved; apparently full of imagery resulting from the hypnotic suggestion.
Similar effects have been shown in previous studies investigating hypnosis’ effect on Stroop Interference.